1. Field of the Invention
The present invention relates to new polyamines, to a method for their preparation and to their use, optionally after neutralization with carboxylic acids, in combination with polyisocyanates as binders for aqueous coating compositions.
2. Description of the Prior Art
Aqueous two-component coating compositions are known and described, for example, in EP-A 0,358,979 (polyacrylate polyol dispersion and polyisocyanate), DE-A 4,129,951 (polyester or polyacrylate dispersion with a hydrophilic reactive thinner and polyisocyanate), DE-A 4,135,571 (dispersion of a mixture of hydrophilic polyester and hydrophilic polyacrylate, combined with a polyisocyanate), DE-A 4,226,242 (polyester dispersion and polyisocyanate), EP-A 0,443,138 (water dispersible polyisocyanates containing ionic hydrophilic groups), EP-A 0,496,205 (polyester/polyurethane dispersion and polyisocyanate), EP-A 0,540,985 (water dispersible polyisocyanates containing ionic hydrophilic groups), EP-A 0,543,228 (polyester/polyacrylate dispersion and polyisocyanate), EP-A 0,557,844 (emulsion copolymer polyol and polyisocyanate), EP-A 0,639,594 (hydroxy-functional dispersion, at least partially neutralized with polyamines, and polyisocyanate) and EP-A 0,661,320 (cationically stabilized polyacrylate dispersion and polyisocyanate).
EP-A 0,505,889 describes aqueous dispersions of encapsulated polyisocyanates. These are produced by dispersing polyisocyanates in water and adding polyamines containing a plurality of amino groups, so that the polyisocyanate droplets are tightly encapsulated by an urea shell due to reaction. After the destruction of the urea shell around the polyisocyanate droplets, these stable polyisocyanate dispersions can undergo further reactions, e.g., with polyols. Coatings produced from coating compositions containing these polyisocyanate dispersions do not possess satisfactory resistance to water.
Generally, polyamines are not suitable co-reactants for polyisocyanates because a spontaneous reaction takes place with the formation of urea groups.
It has now been found that certain low molecular weight oligoesters which contain an average of 2 to 4 double bonds per molecule, optionally in admixture with other unsaturated compounds, can be reacted with (cyclo)aliphatic diamines by the Michael addition reaction to form polyamines which, optionally after neutralization with carboxylic acids, are water dispersible or water-soluble and can be combined with polyisocyanates, which have optionally been rendered hydrophilic, to form aqueous two-component coating compositions, which have a pot life of several hours. These oligoesters are produced either by the trans-esterification of maleic or fumaric acid di(cyclo)alkyl esters with di-, tri- or tetraols, or by the esterification of maleic anhydride or maleic or fumaric acid with di-, tri- or tetraols and monoalcohols.
Due to the fact that polyamines generally undergo a spontaneous reaction with polyisocyanates, the pot life of these new aqueous two-component coating compositions was completely surprising and could not have been predicted. Coatings prepared from these new coating compositions dry rapidly, are free from bubbles and are resistant to customary solvents and water after curing for only a short time.